Carburizing apparatus



March 6, 1928.

c. L. IPSEN GARBURIZING APPARATUS Filed July 28. 1926 I g? wmm w .n n raw 4m m t M V: [T c H w Patented Mar. 6, 1928.

UNITED STATES PATENT- OFFICE,

CARL L. IPSEN, OF SCHENECTADY, NEW YORK,1ASSIGNOR 10 GENERAL ELECTRIC COMPANY, A CORPORATION.

OF NEW YORK.

c'nn'nunrzme APPARATUS.

Application filed July 28-,

My invention relates to carburizin apparatus and has for its object the provision of Iy invention has particular application to.

the case hardening of various ferrous articles, usually for the purpose of improving their wearing quality. It is common manufacturing practice to make various articles, such as machine parts, from a relatively soft, tough metal which may be easily machined or forged and which has high resistance to shocks, such as low carbon steel, and thereafter case harden the finished articles to ive 1 them the, desired wearing properties. In the case hardening processQthe metal is first carburized to a depth of a few t-housandths or a. few hundredths of outer la er of high carbon steel, and there- 2 after this outer layer is hardened by a suitable heat treatment.

The most common method of carburizing iron is to pack the articles in a carbonaceous substance, such as charcoal, and then heat 2 them for a considerable time to a high temperature. *iThlS process is slow and costly, and furthermore difficult to control to obtain uniform results. It has also been proposed to heat the articles in the presence of a car-- 3 bonace-ous gas generated before being admitted to the heating chamber, or in some cases generated in the heating chamber itself by introducing .therein a suitable liquid containing carbon, such as a hydrocarbon liquid.

5 With this latter method a great deal of difficulty has been experienced due to the clog ging upof the liquid inlet orifice by deposits of carbon remaining u of the liquid when Sllb]80t8d to the high temperatures prevailing in the heating chamber.

More specifically my invention relates in one ofits aspects to means for introducing the liquid containing the carbon into the heating chamber so that diflicultyfrom the clogging of the inlet orifice is avoided. In carrying out my invention, I provide cool,- ing means whereby the structure around the liquid inlet orifice is maintained at a .com

- parativelv low temperature, and as a result the liquid drops free into the heating chamber before decomposition occurs, no detri mentaP deposits o carbon being formed to clog up the orifice.

or a more complete understanding of my invention, reference should be had to. the

an inch to form an on the decomposition 1926. Serial No. 125,548.

sides and bottom. Additional heat refractory bricks 12 are provided at the bottom, these latter bricks extending outward so as to provide a cylindrical space around the side [walls which is filledwith a suitable powdered heat refractory material 13, the entire structure being enclosed in a metallic casing 14.

The opening for the furnace chamber 10 is at the top, this opening being considerably smaller than the chamber 10. It is defined by an annular or washer-shaped member 15 which rests on the side walls 11 of the furnace and is provided with an upwardly turned flange 16, forming a. throat, around its central opening. A washer shaped layer of heat refractory material 17 is placed on the member 15 to secure it, this member 17 fitting against thecasing 14. The flange 16 thusforms a constricted throat or opening co'ncentricwith the chamber 10. A'cylindrical metallic heating receptacle 18, forming a retort is set in the heating chamber, the retort being provided with a peripheral flange 19 at the top which rests on the flange 16 of the furnace. It will be observed that the retort is thus supported on theflange 16 in concentric relation with the heating chamber 10 and spaced somewhat from the bottom of the heating chamber. The dimensions of the furnace and retort, are so chosen that sufiicient space is provided between the side wall of the retort and the wall of the heating chamber for the electric heating units 20. As shown these heating units consist of strips of resistance heating material, such as nickel-chromium alloy, which are hungin loops upon pins 21. secured in the side wall of the furnace. Obviously, any suitable electric heating means may be used, or various other types of heating means, such as gas, may be provided.

The cover 25 for the retort and heating chamber is disk-like in shape. It comprises an outer metallic casing 26 in spaced relation with which is a, metallic disk member 27 which fits tightly over the top of the retort. Preferably a ground seat is formed for the member 27 to assure a tight fit. As shown, the member 27 is secured to the casing 26 by means of a metal tube or pipe 28 and bolts 28 at spaced intervals around the periphery of the member 27. The pipe 28 is cast integral with the member 27, these parts and also the retort 18 preferably being made of a heat resisting material, such as a nickel-chromium alloy. Apertures are formed in the member 27 and the casing registering with the pipe 28 so that an aperture defined by the pipe is formed in the cover 25. The casing is secured to the upper end of the pipe 28 by means of a pipe 28' which screws in the threaded aperture in the upper end of pipe 28, the pipe 28 being provided with a flange which seats on the casing 26. In order to interrupt the conduction of heat from the member 27 to the casing 26, a washer 29 of heat refractory material is provided, this washer resting at its inner edge on the upper'surface of the member 27 and at its outer edge on a circumferential flange 30 secured to the casing 26. Pipes 29 are provided, suitably spaced, for holding the washer 29 seated. The space in the interior of the casing 26 is filled with powdered heat refractory insulating material 31. The casing 14 extends somewhat above the member 17 to provide an annular receptacle or trough for a quantity of sand 31 into which extends the lower annular edge of the casing 26 of the cover. This sand seal is provided for the furnace or heating chamber 10.

A suitable liquid carburizing material is introduced into the retort 18 through a. pipe means of which the or duct 32, forming a nozzle. This pipe 32 extends through the cover 25 and has lts lower end. threaded and screwed into a tapped flanged aperture in the member 27. As shown, the lower end of the pipe 32 extends through the member 27 so as to be substantially flush with the lower face of the member 27. Preferably the pipe 32 extends loosely through the casing 26 so that it can be unscrewed from the member 27 and removed, if desired. A suitable coupling 34 is provided on the upper end of the pipe 32 by pipe is connected to a flexible tube 35 which leads to a suitable elevated tank 36 containing the carburizing liquid. A valve 37 is provided in the coupllng 34 by means of which the liquid can be shut off or its rate of flow regulated.

For the purpose of cooling the fluid inlet pipe 32, means 15 provided for circulating a suitable cooling medium around its exterior. As shown, a metallic pipe 38 is wrapped in a helix around the pipe 32, the two ends 39 and 40 of the pipe extending from the cover25. The end 40 of the pipe, for example, is connected to a suitable source of cooling fluid, such as a city water main 41, the other outlet of the pipe 39 being connected to a suitable drain.

By means of this cooling arrangement, I have found that the orifice of the pipe 32 may be maintained at such a comparatively low temperature that the carburizing liquid drops substantially free of the pipe before vaporization sets in, and consequently no agpreciable residue of carbon is left around t e orifice. I have found that with the cooled inlet nozzle the furnace may be operated for an indefinite period of time without detrimental deposits of carbon around the inlet orifice for the carburizing liquid.

In order to facilitate the removal of the cover 25, the cover may be supported on an arm 42 which is 'pivoted on a bracket 43 secured to the casing 14 in such manner that it can be swung about a vertical pivot 44. A supporting member 45 is secured to the cover 25 at the center thereof, and at its upper end this member 45 extends between two projections on the forked end of the arm 42 and is provided with a suitable pivot bearing 46 which rests on an arm 47 extending lengthwise on top of the arm 42. This arm 47 has a pivotal support 48 at one end of the arm 42 at a point adjacent the pivot point of the arm 42. A bell crank lever 49 is pivoted at point 50 on the outer end of the arm42. The longer arm of this bell crank extends upward when the cover is in position on the furnace, as shown in the drawing, and this end terminates in a suitable handle 51. The shorter arm of the hell crank lever lies between the forked projections of the arm 42 and termi nates in a roller bearing 52 located just below the arm 47. \Vhen it is desired to remove the cover the operator grasps the handle 51 and pulls the arm 49 down to a substantially horizontal position which lifts the roller 52 about the ivot 50, whereby the end of the arm 47 is li ted and with it the cover 25. The cover now may be swung on the arm 42 to one side to uncover the furnace. This operating means for the cover is described and claimed in a copending application of Albert N. Otis, Serial No. 44,106, filed July 6, 1925, assigned to the same assignee as this invention.

In carrying out the carburizing recess the material to be carburized is placed in the retort 18 of the furnace and heated to a suitable carburizing temperature, which may be approximately 1700" F. The temperature of the charge may be determined by means of a suitable temperature indicator, such as a thermo-couple 53 inserted through the side wall of the furnace into close proximity with the retort. When the charge has been heated to the carburizing temperature, the valve 37 is opened to allow the carbunzing liquid to run slowly into the retort where it is quickly gasified by the high temperature. The carburizing liquid preferably is fed into'the retort continuously throughout the carburizing period of from one to six hours depending upon the depth of penetration of carbon desired. a Sufiicient liquid is admitted to the retort to maintain a slight gas pressure so that air is excluded. The temperature of the retort is preferably maintained constant by means of suitable automatic control mechanism associated with the electrio heating circuit. After the desired degree of arburization has been obtained,

which may be regulated by the length of time as determined by revious experiments, the charge is removed rom the furnace. It is ordinarily desirable to give the charge aheat treatmentafter carburization in order to cause diffusion inward of the carbon and thus lower the carbon content at the surface to the desired value. I This heat treatment may be carried out in the carburizing furnace, the supply of liquid, of course, being shut off. In some cases the charge may be escape of gas from the pipe 28.

quenched and hardened immediately, but it may be allowed to cool slowly and thereafter heated and quenched to harden it as desired. Y r

Any suitable liquid containing carbon may be used as the carburizing liquid such, for

example, as bone oil or a mixture of cotton-, seed oil and bone oil, as described and claimed in a. co-pending application, Serial No. 131,772 of George W. Hegel and Gerald R. Brophy, filed August .26, 1926 and assigned to the same assignee as this inven tion. As previously stated the supply of liquid is regulated so as to maintain a s ght gas pressure in the retort whereby air is excluded This condition is indicated by If desired, the gas may be ignited. The liquid ordinarily;runs in a. ver small stream or drips drop by drop from t e orifice of the pipe 32.

- The amount of li uid used seems to bear but little relation to t e size of the charge in the retort, which is probably due to the fact that only a small part of the carbon content vof the carburizing liquid is actually used in carburizing the charge. The important thing is to maintain the carburizing atmosf v phere which condition is indicatedby the escape of gas from the pipe 28". In view of the slow rate at which the liquid is admitted to the retort the pipe 32 may be quite small. I have found that a' inch pipe gives very satisfactory operation. The cool-j ing pipe '38-wrapped around it may be somewhat smaller, the requirement being that it shall be sufficiently large to provide for the circulation of the necessary amount of cooling water at a convenient pressure to main- .tain the pipe 3? at the desire reduced temperature.

While I have described my invention as embodied in concrete form and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that I do not limit my invention thereto since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention the scope 0 which is set forth in the annexed claims. a

What I claim as new and desire to secure by Letters Patent of the United States, is

'1. Apparatus for carburizing metals comprising a heating chamber for the charge, means for heating said chamber to a temperature above the critical temperature of the metal to be carburized, a duct .for supplying a carbonaceous liquid to said chamber, a pi e wrapped around said duct thropgh w ich a cooling fluid is passed toprevent deposits ofcarbon on said duct.

2. Carburizing apparatus comprising an electric furnace having a top opening, a retort set in said opening, a cover for said retort, an inlet nozzle secured to said cover,

and a pipe wrapped around said nozzle through which a cooling fluid is passed to I L In Witness whereof, I have hereunto set' of July, 1926.

my hand this 26th day v p CARLL. IPSEN.

a helix ,sur-' 

